WO2022165676A1

WO2022165676A1 - Positive plate and electrochemical apparatus including positive plate, and electronic apparatus

Info

Publication number: WO2022165676A1
Application number: PCT/CN2021/075101
Authority: WO
Inventors: 程世杨; 下羽淳平; 郎野
Original assignee: 宁德新能源科技有限公司
Priority date: 2021-02-03
Filing date: 2021-02-03
Publication date: 2022-08-11
Also published as: CN113795953A

Abstract

Provided are a positive plate, an electrochemical apparatus and an electronic apparatus. The positive plate comprises a positive active material layer, wherein element content on a surface of the positive active material layer satisfies: the molar ratio of manganese to phosphorus ranging from 70:1 to 450:1. The electrochemical apparatus comprises the positive plate. The electronic apparatus comprises the electrochemical apparatus. The positive plate has a relatively good interface stability in an electrolyte, and the high-temperature storage and high-temperature cycle performance of the electrochemical apparatus can be significantly improved.

Description

Positive electrode sheet and electrochemical device and electronic device comprising the same

technical field

The present application relates to the technical field of energy storage, and in particular, to a positive electrode sheet, an electrochemical device and an electronic device including the positive electrode sheet.

Background technique

With the popularity of consumer electronic products such as notebook computers, mobile phones, tablet computers, power banks and drones, the requirements for electrochemical devices (such as lithium-ion batteries) in them are becoming more and more stringent. For example, not only lithium-ion batteries are required to have higher specific capacity, but also lithium-ion batteries are required to be stable in high-temperature environments. However, the current lithium-ion battery has a serious specific capacity degradation at high temperature. This is because the high temperature promotes the occurrence of side reactions in the lithium-ion battery, resulting in the destruction of the electrode active material structure, which affects the stability and service life of the lithium-ion battery. Therefore, there is an urgent need for a lithium-ion battery with a long service life even at high temperatures.

SUMMARY OF THE INVENTION

The purpose of the present application is to provide a positive electrode sheet, an electrochemical device and an electronic device including the positive electrode sheet, so as to improve the stability of the electrochemical device in a high temperature environment.

In some embodiments, the present application provides a positive electrode sheet, which includes a positive electrode active material layer, and the element content on the surface of the positive electrode active material layer satisfies: the molar ratio of manganese element and phosphorus element ranges from 70:1 to 450: 1. In some embodiments, the molar ratio of elemental manganese and elemental phosphorus ranges from 70:1 to 200:1.

In some embodiments, the thickness of the positive electrode active material layer is H, and the molar ratio of phosphorus element and manganese element on the surface of the positive electrode active material layer is _Po ; The molar ratio of phosphorus element and manganese element in the H/4 to H/3 depth region of the layer surface is P _i , and P _o /P _i is 0.5 to 2. In some embodiments, P _o /P _i is 1 to 1.38.

In some embodiments, in the XRD pattern of the surface of the positive electrode active material layer, _IA represents the characteristic peak intensity in the range of 20° to 21°, and _IB represents the characteristic peak intensity in the range of 18° to 18.6°, 0.12≤I _A /I _B ≤0.2.

In some embodiments, the positive electrode active material layer includes a positive electrode active material and a phosphorus-containing compound, the average particle size of the positive electrode active material is D1, and the average particle size of the phosphorus-containing compound is D2, 0.33≤D1/D2 ≤100. In some embodiments, 2≤D1/D2≤100.

In some embodiments, the surface of the positive electrode active material has the phosphorus-containing compound, and the phosphorus-containing compound has a thickness h of 10 nm to 30 nm.

In some embodiments, the average particle diameter D1 of the positive electrode active material is 2 μm to 30 μm, and the average particle diameter D2 of the phosphorus-containing compound is 0.1 μm to 30 μm. In some embodiments, D1 is 10 μm to 25 μm and D2 is 0.1 μm to 5 μm.

In some embodiments, the phosphorus-containing compound includes A _x PO _y , wherein A includes at least one of Li, Na, K, Mg, Ca, Y, Sr, Ba, Zn, Al, or Si, and 1≤x ≤4, 3≤y≤4.

In some embodiments, the positive active material includes at least one of compound a) or compound b): compound a) Li _x1 Mn _2-y1 Z _y1 O ₄ , where Z includes Mg, Al, B, At least one of Cr, Ni, Co, Zn, Cu, Zr, Ti or V, 0.8≤x1≤1.2, 0≤y1≤0.1; compound _b ) Li _x2 Ni _y2 Co _z Mn _k M _q O _ba Ta , where M includes B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, At least one of Sb or Ce; T is halogen, and x2, y2, z, k, q, a and b satisfy: 0.2≤x2≤1.2, 0≤y2≤1, 0≤z≤1, 0< k≤1, 0≤q≤1, 1<b≤2, and 0≤a≤1.

In some embodiments, the mass ratio of the positive electrode active material to the phosphorus-containing compound is 95-97:0.5-3.

In some embodiments, the present application also provides an electrochemical device, the electrochemical device comprising the aforementioned positive electrode sheet of the present application.

In some embodiments, the present application further provides an electronic device, and the electronic device includes the aforementioned electrochemical device of the present application.

The technical solution of the present application has at least the following beneficial effects: when the molar ratio of manganese element and phosphorus element on the surface of the positive electrode active material layer satisfies the range of 70:1 to 450:1, the interface stability of the manganese-containing positive electrode sheet in the electrolyte can be improved It can significantly improve the high-temperature storage and high-temperature cycling performance of electrochemical devices.

Description of drawings

Fig. 1a is the Raman spectrum of the positive electrode sheet used in the lithium ion battery of Example 1, respectively in the fresh state, after formation and after storage; Fig. 1b is the positive electrode used in the lithium ion battery of Comparative Example 1. Raman spectra of the slices in fresh state, after formation and after storage;

Figure 2 is the P spectrum of the EDX-Mapping of the surface of the positive electrode active material layer of the positive electrode sheet measured by the SEM-EDX method after dismantling the lithium-ion battery; wherein, the control group in Figure 2 corresponds to the positive electrode of Comparative Example 1 sheet, the experimental group in Figure 2 corresponds to the positive electrode sheet of Example 1;

Fig. 3 is the XRD pattern of the surface of the positive electrode active material layer of the positive electrode sheet after disassembling the lithium ion batteries of Example 1 and Comparative Example 1 after formation.

Detailed ways

It is to be understood that the disclosed embodiments are merely exemplary of the application, which may be embodied in various forms, and therefore that specific details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as A representative basis is provided for teaching one of ordinary skill in the art to variously implement the application.

For the sake of brevity, only some numerical ranges are expressly disclosed herein. However, any lower limit can be combined with any upper limit to form an unspecified range: and any lower limit can be combined with any other lower limit to form an unspecified range, and likewise any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, every point or single value between the endpoints of a range is included within the range, even if not expressly recited. Thus, each point or single value may serve as its own lower or upper limit in combination with any other point or single value or with other lower or upper limits to form a range not expressly recited.

In this application, the average particle size refers to the observation of the material powder by SEM scanning electron microscope, and then, using image analysis software, 10 material particles are randomly selected from the SEM photograph, and the particle size of each of these material particles is calculated. Area, then, assuming that the material particles are spherical, the respective particle diameters R (diameter) are obtained by the following formula: R=2×(S/π) ^1/2 ; where S is the area of the material particles; for 10 SEMs The image is processed to obtain the particle diameter R of the material particles, and the particle diameters of the obtained 100 (10×10) material particles are arithmetically averaged to obtain the average particle diameter of the material particles.

[Positive plate]

A first aspect of an embodiment of the present application provides a positive electrode sheet.

In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is provided on the surface of the positive electrode current collector. In some embodiments, the positive electrode current collector is a metal, such as, but not limited to, aluminum foil. In some embodiments, manganese element and phosphorus element are included in the positive electrode active material layer.

When the positive electrode active material layer contains manganese element, at least a part of the manganese element usually exists in the form of Mn ³⁺ , such as lithium manganate-based materials, nickel-cobalt lithium manganate-based materials. Since the electrolyte of an electrochemical device usually contains a trace amount of water, the water easily reacts with the lithium salt LiPF ₆ in the electrolyte to form HF. Under the action of HF, Mn ³⁺ is prone to disproportionation reaction to form Mn ⁴⁺ and Mn ^{2 +} ; on the one hand, Mn ²⁺ is easily dissolved, especially at high temperature, the dissolution is further accelerated, and the particle structure of the positive electrode material is destroyed during the dissolution process. On the other hand, the Mn ²⁺ dissolved in the electrolyte during the charging process diffuses from the positive electrode to the In the negative electrode, manganese is deposited on the surface of the negative electrode in the form of metal, destroying the SEI film on the surface of the negative electrode. The positive electrode active material layer of the present application contains phosphorus element, which can complex HF, thereby significantly reducing the content of HF in the electrolyte and improving the stability of the electrochemical device; at the same time, the present application sets the element content on the surface of the positive electrode active material layer. The molar ratio of manganese and phosphorus is in the range of 70:1 to 450:1, and in some embodiments, the molar ratio of manganese and phosphorus is in the range of 70:1 to 200:1. The surface of the positive electrode active material layer in this application refers to the surface of the positive electrode active material layer that is far from the current collector. By controlling the amount of phosphorus on the surface of the positive electrode active material layer to meet a certain range, the surface of the positive electrode active material layer can be fully complexed near the surface of the positive electrode active material layer. HF can prevent manganese from dissolving in the electrolyte, which can improve the stability of the electrochemical device under high temperature conditions and prolong the service life of the electrochemical device. When the content of phosphorus element is higher than this range, the resistance of the surface of the positive electrode active material layer is too large; when the content of phosphorus element is lower than this range, the improvement effect of high temperature performance is not good.

In the embodiments of the present application, the content of manganese element and phosphorus element on the surface of the positive electrode active material layer can be measured by any method known in the art that can measure the content of manganese element and phosphorus element. In some embodiments, the present application can use the following SEM-EDX test method for measurement: first select an area of size 200 μm×200 μm in the SEM-EDX picture of the surface of the positive electrode active material layer, and test the number of P atoms N ₁ in the entire area ; Then measure the number of Mn atoms N ₂ in the area; the molar ratio of Mn/P in the area is W ₁ =N ₂ /N ₁ .

In the embodiments of the present application, the preparation method of the positive electrode active material layer is not particularly limited, and a preparation method known to those skilled in the art may be adopted. For example, the positive electrode active material layer can be prepared by mixing a positive electrode active material containing an Mn element and a phosphorus-containing compound in a positive electrode slurry, and then coating the positive electrode slurry on a positive electrode current collector. Among them, when preparing positive electrode active material layers with different concentrations of phosphorus-containing compounds in the thickness direction, the difference in deposition rate and filling property caused by the difference in density and particle size between phosphorus-containing compounds and positive electrode active materials can be used. The drying temperature and rate are controlled so that phosphorus-containing compounds have different concentrations in the thickness direction of the positive electrode active material layer. In addition, positive electrode active material layers with different concentrations of phosphorus-containing compounds in the thickness direction can also be prepared by layered coating. Layered coating refers to coating the positive electrode slurry layer by layer on the positive electrode current collector. The ratio of the positive electrode active material and the phosphorus-containing compound in the positive electrode slurry can be the same or different. Differences in the content of phosphorus-containing compounds in the thickness direction.

In some embodiments, the thickness of the positive electrode active material layer is H, the molar ratio of phosphorus element and manganese element on the surface of the positive electrode active material layer is P _o , and the distance between the positive electrode active material layer and the positive electrode active material layer is P o . The molar ratio of phosphorus element and manganese element in the H/4 to H/3 depth region of the layer surface is P _i , and P _o /P _i is 0.5 to 2. While ensuring that the amount of phosphorus on the surface of the positive electrode active material layer satisfies a certain range, there is also a considerable amount of phosphorus in the interior near the surface, which can reduce side reactions inside the positive electrode active material layer and further improve the high temperature stability of the electrochemical device. sex. In some embodiments, P _o /P _i is 1 to 1.38.

In the embodiments of the present application, the molar ratio of phosphorus element and manganese element on the surface of the positive electrode active material layer is P _o , and the molar ratio of phosphorus element and manganese element in the depth region of H/4 to H/3 from the surface of the positive electrode active material layer is P o . The molar ratio is _Pi , which can be measured by any method known in the art that can measure the content of phosphorus and manganese. In some embodiments, the application can be measured by the following SEM-EDX test method: In the SEM-EDX picture of the surface of the material layer, an area of 200 μm × 200 μm is selected, and the molar ratio P _o of phosphorus and manganese elements in the entire area is tested; In the SEM-EDX image of the depth area, an area of 200 μm × 200 μm was selected, and the molar ratio _Pi of phosphorus and manganese elements in the entire area was tested; the ratio of the two was P _o /P _i .

In the examples of the present application, when the positive electrode active material layers with different concentrations of phosphorus-containing compounds in the thickness direction are prepared by layered coating, the positive electrode slurry with low phosphorus-containing compound ratio is firstly coated, and then the positive electrode slurry containing phosphorus-containing compounds is coated. The positive electrode slurry with a high phosphorus compound ratio can obtain a P _o /P _i value greater than 1 and less than or equal to 1.38.

In some embodiments, the positive electrode active material layer includes a positive electrode active material. In some embodiments, the positive active material includes at least one of compound a) or compound b): compound a) Li _x1 Mn _2-y1 Z _y1 O ₄ , where Z includes Mg, Al, B, At least one of Cr, Ni, Co, Zn, Cu, Zr, Ti or V, 0.8≤x1≤1.2, 0≤y1≤0.1; compound _b ) Li _x2 Ni _y2 Co _z Mn _k M _q O _ba Ta , where M includes B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga, Y, Zr, Mo, Ag, W, In, Sn, Pb, At least one of Sb or Ce; T is halogen, and x2, y2, z, k, q, a and b satisfy: 0.2≤x2≤1.2, 0≤y2≤1, 0≤z≤1, 0< k≤1, 0≤q≤1, 1<b≤2, and 0≤a≤1.

The manganese element is added to the positive electrode active material layer in the form of a lithium manganate-based positive electrode active material and/or a ternary positive electrode active material. Lithium manganate materials (Li _x1 Mn _2-y1 Z _y1 O ₄ ) have high theoretical specific capacity and high safety performance as cathode active materials for lithium ion batteries. High cost performance for commercialization, however, lithium manganate materials have serious specific capacity decay during charge and discharge, especially at high temperatures (above 60°C). It can avoid the disproportionation reaction of Mn ³⁺ in the lithium manganate material, avoid the formation of Mn ²⁺ , so as to avoid the destruction of the structure of lithium manganate, and avoid the occurrence of Jahn during the charging and discharging process of the spinel lithium manganate. -Teller effect, avoid crystal distortion when manganese valence is lower than +3.5, so as to avoid lattice distortion caused by the transformation from cubic phase to tetragonal phase, and effectively solve the problem of specific capacity attenuation of lithium manganate materials at high temperature. question.

Phosphorus element is added to the positive electrode active material layer in the form of a phosphorus-containing compound. In some embodiments, the cathode active material layer includes a phosphorus-containing compound, the phosphorus-containing compound includes A _x PO _y , wherein A includes Li, Na, K, Mg, Ca, Y, Sr, Ba, Zn, At least one of Al or Si, 1≤x≤4, 3≤y≤4.

In some embodiments, the average particle size of the positive electrode active material is D1, and the average particle size of the phosphorus-containing compound is D2, 0.33≤D1/D2≤100. When the positive electrode active material and the phosphorus-containing compound meet the above conditions, the phosphorus-containing compound can be uniformly dispersed in the positive electrode active material layer. When D1/D2<0.33, the particle size of the phosphorus-containing compound is relatively too large, resulting in the positive electrode active material layer. The phosphorus-containing compounds are difficult to distribute evenly, and the stability is poor locally due to the lack of effective protection of phosphorus-containing compounds; and when D1/D2>100, the particle size of phosphorus-containing compounds is relatively too small, and during the coating process, the It will be more deposited in the lower layer of the positive active material layer and filled in the pores between the positive active materials, resulting in the lack of effective protection of the phosphorus-containing compound on the surface of the positive active material layer, and the small particle size of the phosphorus-containing compound is easy to agglomerate, It is also difficult to disperse uniformly.

In some embodiments, the surface of the positive electrode active material has the phosphorus-containing compound, and the phosphorus-containing compound has a thickness h of 10 nm to 30 nm. When the positive electrode active material and the phosphorus-containing compound meet the above conditions, a solid solution interface is formed between the phosphorus-containing compound and the positive electrode active material, which can effectively protect the surface of the positive electrode active material and avoid the problem of impedance increase caused by excessive thickness. During preparation, the positive electrode active material precursor, the lithium source and the phosphorus-containing compound are uniformly mixed by means of high-speed mechanical mixing, and sintered to obtain a positive electrode active material whose surface is coated with the phosphorus-containing compound.

In some embodiments, the average particle diameter D1 of the positive electrode active material is 2 μm to 30 μm. In some embodiments, the phosphorus-containing compound has an average particle size D2 of 0.1 μm to 30 μm.

In some embodiments, the average particle diameter D1 of the positive electrode active material is 10 μm to 25 μm. In some embodiments, the phosphorus-containing compound has an average particle size D2 of 0.1 μm to 5 μm.

The mass ratio of the positive electrode active material to the phosphorus-containing compound affects the distribution of manganese and phosphorus elements in the positive electrode active material layer, and when the mass ratio of the positive electrode active material to the phosphorus-containing compound meets a certain range, it is beneficial to adjust the phosphorus element in the positive electrode active material. The distribution in the layer promotes the complexation of P and HF, and further improves the high temperature stability of the electrochemical device. In some embodiments, the mass ratio of the positive electrode active material to the phosphorus-containing compound is 95-97:0.5-3.

In some embodiments, in the XRD pattern of the surface of the positive electrode active material layer, _IA represents the characteristic peak intensity in the range of 20° to 21°, and _IB represents the characteristic peak intensity in the range of 18° to 18.6°, 0.12≤I _A /I _B ≤0.2. Wherein, the characteristic peak intensity in the range of 20° to 21° corresponds to the content of phosphorus-containing compounds in the positive electrode active material layer, and the characteristic peak intensity in the range of 18° to 18.6° corresponds to the content of lithium manganate in the positive electrode active material layer, The positive electrode active material layer with this characteristic peak intensity ratio indicates that the surface of the positive electrode active material layer has a sufficient amount of phosphorus-containing compounds, which can reduce the damage of HF to the positive electrode active material.

In some embodiments, the positive electrode active material layer further includes a positive electrode binder. The positive electrode binder is used to improve the bonding properties between the positive electrode active material particles and between the positive electrode active material particles and the positive electrode current collector. The positive electrode binder is known in the art as a binder that can be used as a positive electrode active material layer. In some embodiments, the positive binder includes polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl Ethoxylated polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (esterified) styrene-butadiene rubber, epoxy resin, nylon at least one of.

In some embodiments, the positive electrode active material layer further includes a positive electrode conductive agent. The positive electrode conductive agent is used to improve the conductivity of the positive electrode sheet. The positive electrode conductive agent is a conductive agent known in the art that can be used as the positive electrode active material layer. In some embodiments, the positive electrode conductive agent includes at least one of graphite, conductive carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, metal powder, and metal fiber. In some embodiments, the metal in the metal powder and metal fibers includes at least one of copper, nickel, aluminum, and silver.

The present application has no particular restrictions on the mixing ratio of the positive electrode active material, the positive electrode binder, and the positive electrode conductive agent in the positive electrode active material layer, and the mixing ratio can be controlled according to the desired electrochemical device performance.

[Electrochemical device]

A second aspect of an embodiment of the present application provides an electrochemical device. The electrochemical device of the present application is, for example, a primary battery or a secondary battery. The secondary battery is, for example, a lithium secondary battery, and the lithium secondary battery includes, but is not limited to, a lithium metal secondary battery, a lithium ion secondary battery, a lithium polymer secondary battery, or a lithium ion polymer secondary battery. In some embodiments, the electrochemical device includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, and the positive electrode sheet is the positive electrode sheet of the first aspect of the application.

In some embodiments, after the electrochemical device is discharged to 25% state of charge, it is stored at 80° C. for 1 day. Mann test, there are two peaks in the wavelength range of 258-846cm ^-1 , the ratio of the strongest peak to the second strongest peak is: 1.6~2.0, indicating that the surface layer lithium manganate still has the initial crystal structure and is well protected .

Negative plate

The negative electrode sheet is a negative electrode sheet known to those skilled in the art that can be used in an electrochemical device. In some embodiments, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer. The negative electrode active material layer is provided on the surface of the negative electrode current collector.

In some embodiments, the negative current collector is a metal such as, but not limited to, copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, a conductive metal clad polymer substrate, or a combination thereof.

In some embodiments, the anode active material layer includes an anode active material. The negative electrode active material can be selected from various conventionally known materials capable of intercalating and deintercalating active ions or conventionally known materials capable of doping and dedoping active ions, which are known in the art and can be used as electrochemical devices. In some embodiments, the negative active material includes at least one of carbon material, silicon material, lithium metal, lithium metal alloy, transition metal oxide. In some embodiments, the carbon material includes at least one of natural graphite, artificial graphite, soft carbon, hard carbon, mesophase pitch carbonization product, fired coke.

In some embodiments, the anode active material layer further includes an anode binder. The negative electrode binder is used to improve the bonding properties between the negative electrode active material particles and between the negative electrode active material particles and the negative electrode current collector. The negative electrode binder is known in the art and can be used as a binder for the negative electrode active material layer. In some embodiments, the negative electrode binder includes polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl Ethoxylated polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy At least one of resin and nylon.

In some embodiments, the negative electrode active material layer further includes a negative electrode conductive agent. The negative electrode conductive agent is used to improve the conductivity of the negative electrode sheet. The negative electrode conductive agent is a conductive agent known in the art that can be used as the negative electrode active material layer. In some embodiments, the negative electrode conductive agent includes at least one of conductive carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotube, graphene, metal powder, metal fiber, and polyphenylene derivatives. In some embodiments, the metal in the metal powder and metal fiber includes at least one of copper, nickel, aluminum, and silver.

In some embodiments, the preparation method of the negative electrode sheet is known in the art for the preparation method of the negative electrode sheet that can be used in an electrochemical device. In some embodiments, in the preparation of the negative electrode slurry, a solvent, a negative electrode active material and a negative electrode binder are usually added, and a negative electrode conductive agent and a thickening agent are added as required to prepare the negative electrode slurry. The solvent is evaporated and removed during the drying process. The solvent is known in the art and can be used as the negative electrode active material layer, such as but not limited to water, N-methylpyrrolidone. Thickeners are known in the art that can be used as the negative electrode active material layer, such as, but not limited to, sodium carboxymethyl cellulose. The present application has no particular restrictions on the mixing ratio of the negative electrode active material, negative electrode binder, negative electrode conductive agent, and thickener in the negative electrode active material layer, and the mixing ratio can be controlled according to the desired performance of the electrochemical device.

Electrolyte

Electrolytes are electrolytes known in the art that can be used in electrochemical devices. In some embodiments, the electrolyte includes an organic solvent, an electrolyte salt, and additives.

The organic solvent may be an organic solvent known in the art that can be used for the electrolyte. In some embodiments, the organic solvent includes ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), propylene carbonate At least one of ester and ethyl propionate.

The electrolyte salt may be an electrolyte salt known in the art that can be used in the electrolyte. In some embodiments, the electrolyte salt is a lithium salt, and the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium difluorophosphate (LiPO ₂ F ₂ ), lithium bistrifluoromethanesulfonimide LiN (CF ₃ SO _{2 )} ) ₂ (LiTFSI), Lithium Bis(fluorosulfonyl)imide Li(N(SO ₂ F) ₂ )(LiFSI), Lithium Bisoxalate Borate LiB(C ₂ O ₄ ) ₂ (LiBOB), and Lithium Difluorooxalate Borate At least one of LiBF ₂ (C ₂ O ₄ ) (LiDFOB). In some embodiments, the lithium salt includes lithium hexafluorophosphate (LiPF ₆ ). In some embodiments, based on the volume of the electrolyte, the molar concentration of lithium in the lithium salt is about 0.5 mol/L to about 3 mol/L, about 0.5 mol/L to about 2 mol/L, or about 0.8 mol/L L to about 1.5 mol/L.

The additives may be those known in the art that may be used in the electrolyte.

In some embodiments, the positive electrode sheet is placed in an electrolyte with a volume ratio of ethylene carbonate to dimethyl carbonate of 3:7 and a LiPF ₆ concentration of 1M, wherein the positive electrode contained in the positive electrode sheet The mass ratio of the active material layer to the volume of the electrolyte is 1 g/100mL. After soaking at 80°C for 1 day, the mass percentage z of Mn and Li elements contained in the electrolyte is ≤ 0.5%, indicating that due to the presence of HF is complexed by phosphorus element, and Mn element is less dissolved in the electrolyte, so the electrochemical device has high high temperature stability.

isolation film

Separation membranes are well known in the art that can be used in electrochemical devices. The separator is arranged between the positive electrode sheet and the negative electrode sheet for preventing short circuit.

The present application has no particular limitations on the material and shape of the separator. In some embodiments, the separator includes a polymer or inorganic formed from a material that is stable to the electrolyte of the present application.

In some embodiments, the release film includes a substrate layer and a surface treatment layer disposed on at least one surface of the substrate layer.

In some embodiments, the substrate layer is a non-woven fabric, membrane or composite membrane with a porous structure. In some embodiments, the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. In some embodiments, the substrate layer is selected from any one of polypropylene porous membrane, polyethylene porous membrane, polypropylene non-woven fabric, polyethylene non-woven fabric or polypropylene-polyethylene-polypropylene porous composite membrane.

In some embodiments, the surface treatment layer is a polymer layer or an inorganic layer, or a layer formed by mixing polymers and inorganic substances. In some embodiments, the inorganic layer includes inorganic particles and a binder, the inorganic particles are selected from the group consisting of aluminum oxide, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, ceria, nickel oxide, zinc oxide, One or a combination of calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide and barium sulfate, and the binder is selected from polyvinylidene fluoride, Vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene One or a combination of ethylene and polyhexafluoropropylene. In some embodiments, the polymer layer comprises a polymer selected from the group consisting of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl ether, polyvinyl At least one of vinylidene fluoride or poly(vinylidene fluoride-hexafluoropropylene).

outer packaging shell

In some embodiments, the electrochemical device further includes an overpack housing. Overpack casings are known in the art that can be used in electrochemical devices and are stable to the electrolyte used, such as, but not limited to, metal-type overpack casings.

[electronic device]

A third aspect of the embodiments of the present application provides an electronic device. The electronic device of this application is any electronic device, such as but not limited to notebook computers, pen-type computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, headsets, video recorders , LCD TV, Portable Cleaner, Portable CD Player, Mini Disc, Transceiver, Electronic Notepad, Calculator, Memory Card, Portable Recorder, Radio, Backup Power, Motor, Automobile, Motorcycle, Power-assisted Bicycle, Bicycle, Lighting Appliances, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, lithium-ion capacitors. It should be noted that the electrochemical device of the present application is not only applicable to the electronic devices exemplified above, but also applicable to energy storage power stations, marine vehicles, and air vehicles. Airborne vehicles include airborne vehicles within the atmosphere and airborne vehicles outside the atmosphere.

In some embodiments, the electronic device comprises the electrochemical device of the second aspect of the present application.

The present application will be further described below with reference to the embodiments. It should be understood that these examples are only used to illustrate the present application and not to limit the scope of the present application.

In the following examples and comparative examples, the used reagents, materials and instruments can be obtained commercially or synthetically unless otherwise specified.

Example 1

(1) Preparation of electrolyte

Under a dry argon atmosphere, the organic solvents propylene carbonate (PC), ethylene carbonate (EC), and diethyl carbonate (DEC) were mixed uniformly in a weight ratio of 1:1:1, and fully dried lithium salt LiPF ₆ was added. After being dissolved in the above organic solvent and fully mixed, an electrolyte solution with a lithium salt concentration of 1.15 mol/L was obtained.

(2) Preparation of positive electrode sheet

The positive electrode active material LiMn ₂ O ₄ (average particle size D1 is 10 μm), phosphorus-containing compound Al(PO ₃ ) ₃ (average particle size D2 is 5 μm), conductive agent conductive carbon black (Super P), and binder are polarized Vinyl fluoride (PVDF) is mixed according to the weight ratio of 97.5:0.5:1:1, then an appropriate amount of N-methylpyrrolidone (abbreviated as NMP) is added as a solvent, and the mixture is fully stirred and mixed to obtain a solid content of 75% and a viscosity of 5000mPas cathode slurry.

Then, the positive electrode slurry was evenly coated on the aluminum foil, dried at 80°C and rolled, and the thickness of the positive electrode active material layer on one side was 40 μm. Repeat the above steps on the other surface of the positive electrode sheet to obtain a positive electrode coated on both sides. piece.

(3) Preparation of separator

A polyethylene (PE) porous polymeric film is used as the separator.

(4) Preparation of negative electrode sheet

The negative active material artificial graphite, binder styrene-butadiene rubber and thickener sodium carboxymethyl cellulose (abbreviated as CMC) are fully stirred and mixed in an appropriate amount of deionized water solvent according to the weight ratio of 96:2:2, so that It forms a uniform negative electrode slurry; the negative electrode slurry is coated on a copper foil with a thickness of 12 μm, dried, cold pressed, and then cut and welded to obtain a negative electrode sheet.

(5) Preparation of lithium ion battery

The prepared positive electrode sheet, separator film and negative electrode sheet are stacked in sequence, so that the separator film is placed between the positive electrode sheet and the negative electrode sheet to play a role of isolation, and then rolled to obtain a bare cell; the bare cell is placed in an outer package In the process, the liquid injection port is left, and the electrolyte prepared above is poured from the liquid injection port.

Example 2

The difference from Example 1 is the preparation of the positive electrode sheet. The weight ratio of positive electrode active material LiMn ₂ O ₄ , phosphorus-containing compound Al(PO ₃ ) ₃ , conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) is 97:1:1:1. After the positive electrode slurry was evenly coated on the aluminum foil, it was quickly dried at 120°C and then rolled.

Example 3

The difference from Example 1 is the preparation of the positive electrode sheet. The weight ratio of positive electrode active material LiMn ₂ O ₄ , phosphorus-containing compound Al(PO ₃ ) ₃ , conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) is 97:1:1:1.

Example 4

The difference from Example 3 is the preparation of the positive electrode sheet. In the method of layered coating, the positive electrode slurry with a low phosphorus-containing compound ratio is first coated on the aluminum foil, and after drying, the positive electrode slurry with a high phosphorus-containing compound ratio is coated, and rolled after drying.

Example 5

The difference from Example 3 is the preparation of the positive electrode sheet. In the method of layered coating, the positive electrode slurry with a high phosphorus-containing compound ratio is firstly coated on the aluminum foil, and after drying, the positive electrode slurry with a low phosphorus-containing compound ratio is coated, and rolled after drying.

Example 6

The difference from Example 1 is the preparation of the positive electrode sheet. The weight ratio of positive electrode active material LiMn ₂ O ₄ , phosphorus-containing compound Al(PO ₃ ) ₃ , conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) is 96.5:1.5:1:1. After the positive electrode slurry was uniformly coated on the aluminum foil, it was dried at 100°C and rolled.

Example 7

The difference from Example 1 is the preparation of the positive electrode sheet. The weight ratio of positive electrode active material LiMn ₂ O ₄ , phosphorus-containing compound Al(PO ₃ ) ₃ , conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) is 95:3:1:1. After the positive electrode slurry was uniformly coated on the aluminum foil, it was dried at 100°C and rolled.

Example 8

The difference from Example 1 is the preparation of the positive electrode sheet. Positive electrode active material LiMn ₂ O ₄ (average particle size D1 is 20 μm), phosphorus-containing compound is LiPO ₃ (average particle size D2 is 5 μm), conductive agent conductive carbon black (Super P), binder polyvinylidene fluoride (PVDF) ) in a weight ratio of 97:1:1:1.

Example 9

The difference from Example 8 is the preparation of the positive electrode sheet. The phosphorus-containing compound was Ce(PO ₃ ) ₃ (average particle diameter D2 was 5 μm).

Example 10

The difference from Example 8 is the preparation of the positive electrode sheet. The positive electrode active material was LiMn ₂ O ₄ (average particle size D1 was 25 μm), and the phosphorus-containing compound was NaPO ₃ (average particle size D2 was 5 μm).

Example 11

The difference from Example 1 is the preparation of the positive electrode sheet. The positive electrode active materials LiMn ₂ O ₄ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (average particle size D1 is 10 μm), phosphorus-containing compound Al(PO ₃ ) ₃ (average particle size D2 is 5 μm), conductive agent conductive carbon black ( Super P) and binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 87.3:7.8:1:1:1.

Example 12

The difference from Example 1 is the preparation of the positive electrode sheet. The weight ratio of positive electrode active material LiNi _0.5 Co _0.2 Mn _0.3 O ₂ , phosphorus-containing compound Al(PO ₃ ) ₃ , conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) is 97:1: 1:1.

Example 13

The difference from Example 2 is the preparation of the positive electrode sheet. Phosphorus-containing compound Al(PO ₃ ) ₃ (average particle diameter D2 is 0.1 μm).

Example 14

The difference from Example 2 is the preparation of the positive electrode sheet. Phosphorus-containing compound Al(PO ₃ ) ₃ (average particle diameter D2 is 0.2 μm).

Example 15

The difference from Example 2 is the preparation of the positive electrode sheet. Phosphorus-containing compound Al(PO ₃ ) ₃ (average particle diameter D2 is 0.5 μm).

Example 16

The difference from Example 2 is the preparation of the positive electrode sheet. The positive electrode active material is LiMn ₂ O ₄ coated with phosphorus-containing compound Al(PO ₃ ) ₃ , and the coating thickness is 20 nm.

Comparative Example 1

The difference from Example 1 is the preparation of the positive electrode sheet. The positive electrode active material LiMn ₂ O ₄ (average particle size D1 is 10 μm), the conductive agent conductive carbon black (Super P), and the binder polyvinylidene fluoride (PVDF) were mixed in a weight ratio of 98:1:1.

Comparative Example 2

The difference from Example 1 is the preparation of the positive electrode sheet. Positive electrode active material LiMn ₂ O ₄ (average particle size D1 is 10 μm), phosphorus-containing compound Al(PO ₃ ) ₃ (average particle size D2 is 0.5 μm), conductive agent conductive carbon black (Super P), binder polypolarization The weight ratio of vinyl fluoride (PVDF) was 94:4:1:1.

Comparative Example 3

The difference from Example 1 is the preparation of the positive electrode sheet. Positive electrode active material LiMn ₂ O ₄ (average particle size D1 is 10 μm), phosphorus-containing compound Al(PO ₃ ) ₃ (average particle size D2 is 5 μm), conductive agent conductive carbon black (Super P), binder polyvinylidene fluoride The weight ratio of ethylene (PVDF) was 94:4:1:1.

Comparative Example 4

The difference from Example 1 is the preparation of the positive electrode sheet. Positive electrode active material LiMn ₂ O ₄ (average particle size D1 is 10 μm), phosphorus-containing compound Al(PO ₃ ) ₃ (average particle size D2 is 0.1 μm), conductive agent conductive carbon black (Super P), binder polypolarization The weight ratio of vinyl fluoride (PVDF) was 97:1:1:1.

Comparative Example 5

The difference from Example 1 is the preparation of the positive electrode sheet. The positive electrode active materials LiMn ₂ O ₄ and LiNi _0.5 Co _0.2 Mn _0.3 O ₂ (average particle size D1 is 10 μm), conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) according to 88.2:9.8 : 1:1 weight ratio mixing.

Test Methods for Lithium Ion Batteries

Element molar ratio test: disassemble the formed lithium-ion battery to obtain a positive electrode sheet, (1) use the SEM-EDX test method to test the distribution of Mn and P elements on the surface of the positive electrode active material layer, and select them from the SEM-EDX image. For an area of 200μm×200μm size, the ratio of the number of Mn atoms to the number of P atoms in the entire area is obtained by testing. (2) The SEM-EDX test method was used to test the surface P element in the positive electrode active material layer and the P element distribution at a depth of 10 μm from the surface. Area, test the molar ratio P _o of phosphorus and manganese elements in the entire area; then select an area of 200 μm × 200 μm in the SEM-EDX picture at a depth of 10 μm from the surface of the positive active material layer, and test the phosphorus in the entire area. The molar ratio P _i of element and manganese element; and then obtain P _o /P _i .

XRD test: Keep the surface of the dried positive electrode sheet flat, place it in the sample stage of an XRD test instrument (Model Bruker, D8), use a scanning rate of 2°/min, and a scanning angle range of 10° to 90° to obtain an XRD pattern.

Average particle size test: Taking the average particle size D2 test of phosphorus-containing compounds as an example, the material powder was photographed and observed by SEM scanning electron microscope, and then, using image analysis software, 10 phosphorus-containing compounds were randomly selected from the SEM photos. particles, obtain the area of each of these phosphorus-containing compound particles, and then, assuming that the material particles are spherical, obtain the respective particle diameters R (diameter) by the following formula: R=2×(S/π) ^1/2 ; where, S is the area of the phosphorus-containing compound particles; 10 SEM images are processed to obtain the particle diameter R of the phosphorus-containing compound particles, and the particle diameters of the obtained 100 (10×10) phosphorus-containing compound particles are arithmetically averaged, so that The average particle diameter D2 of the phosphorus-containing compound particles was obtained.

Raman spectroscopy test: After discharging the lithium-ion battery to 25% SOC, store it at 80°C for 1 day. After dismantling, wash the positive electrode sheet with dimethyl carbonate solvent, dry it at 85°C for 12 hours, and place it on the sample of the Raman testing instrument. Taichung, using a silicon wafer for peak position correction, randomly focusing the point on the positive plate at a long focal length of 10+, there are two peaks in the wavelength range of 258-846cm ^-1 , and taking the ratio of the strongest peak to the second strongest peak; random focusing 10 points, and the average value was recorded as the Raman peak intensity ratio.

Button-down test: Clean one side of the positive electrode active material layer after drying the positive electrode sheet with N-methylpyrrolidone (NMP), bake it in a vacuum at 85°C for 2 hours, and take out the positive electrode for 2025 button battery. , according to the nickel foam, lithium sheet, separator, positive disc, assemble into a button battery, inject 50 microliters of electrolyte, the composition of the electrolyte is EC:PC:DEC=1:1:1, and in the electrolyte The concentration of LiPF ₆ was 1.15 mol/L.

The assembled button battery was charged and discharged at a cut-off voltage of about 2.7 to about 4.3V at 25°C with a current of 0.2C to test its gram capacity, gram capacity=discharge capacity/mass of positive active material.

The assembled button battery was charged at 45°C with a constant current of 0.5C and then discharged with a constant current of 0.5C. After 50 cycles, the ratio of the electricity released by the 50th discharge to the initial discharge capacity was calculated.

Mn/Li content test in the electrolyte : put the positive electrode sheet in the electrolyte with a volume ratio of ethylene carbonate to dimethyl carbonate of 3:7 and a LiPF ₆ concentration of 1M, the mass of the positive active material layer and the volume of the electrolyte The ratio was 1 g/100 mL, and after soaking at 80 °C for 1 day, the electrolyte was filtered through a 450 nm filter head, and the filtrate was measured by a plasma photoelectric direct reading spectrometer (ICP).

High- temperature storage test: discharge the lithium-ion battery to 30% SOC, and the 100% SOC is recorded as the initial capacity; store it in a 60°C oven for 7 days, and then charge and discharge 3 times with a current of 0.2C, and measure the lithium-ion battery at this time. The capacity of the battery is recorded as the capacity recovered after shelving. Recovery capacity retention rate (%) = recovery capacity after shelving/initial capacity.

High temperature cycle test: After the lithium-ion battery is formed, at 45°C, it is charged at a constant current of 0.5C and then discharged at a constant current of 1C. After 500 cycles, the ratio of the amount of electricity released by the 500th discharge to the initial discharge capacity is calculated.

From the data analysis in Table 1, it can be seen that when the molar ratio of manganese element and phosphorus element on the surface of the positive electrode active material layer satisfies the range of 70:1 to 450:1, the interface stability of the manganese-containing positive electrode sheet in the electrolyte can be improved significantly. Improve high temperature storage and high temperature cycling performance of Li-ion batteries. It can be seen from Comparative Examples 2-3 that when the molar ratio of manganese element and phosphorus element on the surface of the positive active material layer is less than 70:1, the surface impedance increases and the cycle performance decreases due to excessive phosphorus-containing compounds on the surface. It can be seen from Comparative Example 4 that when the particle size D2 of the phosphorus-containing compound is smaller than the particle size D1 of the active material, if the drying rate is slow, the phosphorus-containing compound is easy to fill in the gaps between the active materials, thereby enriching in the active material. For the lower layer of the material layer, the molar ratio of manganese element and phosphorus element on the surface cannot meet the requirements, and the high temperature storage and cycle cannot be well improved.

From the data of Example 2 to Example 5, when the total amount of phosphorus elements in the positive electrode active material layer is the same, the distribution of phosphorus elements on the surface of the positive electrode active material layer and near the surface of the positive electrode active material layer affects the performance of lithium ion batteries. . When it is ensured that a considerable amount of phosphorus element exists on the surface of the positive electrode active material layer and the interior near the surface of the positive electrode active material layer, the high temperature storage and high temperature cycle performance of the lithium ion battery can be better improved. Example 4 shows that when Po/Pi is 2, since the content of the internal phosphorus-containing compound near the surface of the positive electrode active material layer is relatively low, it cannot be well protected, and therefore, its high temperature performance is reduced. However, Example 5 shows that when Po/Pi is 0.5, due to the relatively high content of phosphorus-containing compounds near the surface of the positive electrode active material layer, the resistance of the surface layer of the positive electrode active material layer increases, and therefore, its cycle performance decreases.

From the data of Examples 2 and 13-15, it can be obtained that when the average particle size D1 of the positive electrode active material and the average particle size D2 of the phosphorus-containing compound satisfy 0.33≤D1/D2≤100, by controlling the drying rate, the phosphorus-containing compound particles It can be uniformly distributed in the positive electrode active material layer, and ensures that a considerable amount of phosphorus-containing compounds can exist on the surface of the positive electrode active material layer and the interior near the surface of the positive electrode active material layer, which can better improve the high-temperature storage and high-temperature cycle performance of lithium-ion batteries.

It can be seen from the data of Example 16 that when the surface of the positive electrode active material is coated with the phosphorus-containing compound, the high-temperature storage and high-temperature cycle performance of the lithium-ion battery can also be well improved.

Claims

A positive electrode sheet includes a positive electrode active material layer, and the element content on the surface of the positive electrode active material layer satisfies: the molar ratio of manganese element and phosphorus element ranges from 70:1 to 450:1.
The positive electrode sheet according to claim 1, wherein the thickness of the positive electrode active material layer is H, the molar ratio of phosphorus element and manganese element on the surface of the positive electrode active material layer is Po; The molar ratio of phosphorus element and manganese element in the H/4 to H/3 depth region on the surface of the positive electrode active material layer is P i , and P o /P i is 0.5 to 2.
The positive electrode sheet according to claim 2, wherein the positive electrode sheet satisfies at least one of the following conditions:

1) The element content on the surface of the positive electrode active material layer satisfies: the molar ratio of manganese element and phosphorus element ranges from 70:1 to 200:1;

2) P o /P i is 1.0 to 1.38.
The positive electrode sheet according to claim 2, wherein, in the XRD pattern of the surface of the positive electrode active material layer, IA represents the characteristic peak intensity in the range of 20° to 21°, and IB represents the range of 18° to 18.6° The characteristic peak intensity of 0.12≤I A /I B ≤0.2.
The positive electrode sheet according to claim 1, wherein the positive electrode active material layer comprises a positive electrode active material and a phosphorus-containing compound, and satisfies at least one of the following conditions:

i) The average particle size of the positive electrode active material is D1, and the average particle size of the phosphorus-containing compound is D2, 0.33≤D1/D2≤100;

ii) The surface of the positive electrode active material has the phosphorus-containing compound, and the thickness h of the phosphorus-containing compound is 10 nm to 30 nm.
The positive electrode sheet according to claim 5, wherein the D1 is 2 μm to 30 μm, and the D2 is 0.1 μm to 30 μm.
The positive electrode sheet according to claim 5, wherein the phosphorus-containing compound comprises A x PO y , wherein A comprises at least one of Li, Na, K, Mg, Ca, Y, Sr, Ba, Zn, Al or Si , 1≤x≤4, 3≤y≤4.
The positive electrode sheet according to claim 5, wherein the positive electrode active material comprises at least one of compound a) or compound b):

Compound a) Li x1 Mn 2-y1 Z y1 O 4 , where Z includes at least one of Mg, Al, B, Cr, Ni, Co, Zn, Cu, Zr, Ti or V, 0.8≤x1≤ 1.2, 0≤y1≤0.1;

Compound b ) Li x2 Ni y2 Co z Mn k M q O ba Ta , where M includes B, Mg, Al, Si, P, S, Ti, Cr, Fe, Co, Ni, Cu, Zn, Ga At least one of , Y, Zr, Mo, Ag, W, In, Sn, Pb, Sb or Ce; T is halogen, and x2, y2, z, k, q, a and b respectively satisfy: 0.2≤x2 ≤1.2, 0≤y2≤1, 0≤z≤1, 0<k≤1, 0≤q≤1, 1<b≤2, and 0≤a≤1.
An electrochemical device, comprising the positive electrode sheet of any one of claims 1-8.
An electronic device comprising the electrochemical device of claim 9.